1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device which uses an SOI (silicon on insulator) substrate. The present invention particularly relates to a bonding SOI technique, and to a method of manufacturing a semiconductor device which uses an SOI substrate obtained by attaching a single-crystal or polycrystalline semiconductor film to a substrate with an insulating film interposed between the semiconductor film and the substrate.
2. Description of the Related Art
Demands for higher integration, higher operation speed, higher performance, and lower power consumption in semiconductor integrated circuits have been more stringent, and in response to such demands, a transistor using an SOI substrate has attracted attention as effective means that can take place of a bulk transistor. Higher operation speed and lower power consumption can be expected more in a transistor using an SOI substrate than in a bulk transistor because a semiconductor film is formed over an insulating film in a transistor using an SOI substrate, and accordingly parasitic capacitance can be reduced and generation of leakage current flowing through the substrate can be suppressed. In addition, since a semiconductor film used as an active layer can be thinned, a short channel effect can be suppressed; thus, an element can be miniaturized, and accordingly higher integration of semiconductor integrated circuits can be realized. Moreover, since a transistor using an SOI substrate is a completely latch-up free transistor, there is no risk that the element will be broken due to heat caused by latch-up. Furthermore, a transistor using an SOI substrate does not need element isolation unlike a bulk transistor; thus, a transistor using an SOI substrate has advantages in that the distance between the elements can be shortened to achieve higher integration.
As one of methods of manufacturing an SOI substrate, there is a method in which a semiconductor film is attached to a substrate with an insulating film interposed therebetween, such as UNIBOND (registered trademark) typified by Smart-Cut (registered trademark), ELTRAN (epitaxial layer transfer), a dielectric separation method, or a PACE (plasma assisted chemical etching) method. The above-described bonding methods make it possible to form high-performance integrated circuits by using a single crystal semiconductor film, over a glass substrate which is inexpensive.
One of the examples of semiconductor devices using SOI substrates has been disclosed by Patent document 1: Japanese Published Patent Application No. 2000-012864.